1. Field of the Invention
The field of the invention relates to electro-optical readers or scanning systems, such as bar code symbol readers, and more particularly to the optical path design in a scanning module for use in applications requiring both single line and raster scanning in a single, compact bar code reader.
2. Description of the Related Art
Bar code symbols are formed from bars or elements typically rectangular in shape with a variety of possible widths. The specific arrangement of elements defines the characters represented according to a set of rules and definitions specified by the code or xe2x80x9csymbologyxe2x80x9d used. The relative size of the bars and spaces is determined by the type of coding used as is the actual size of the bars and spaces. The number of characters (represented by the bar code symbol) per unit length is referred to as the density of the symbol. To encode the desired sequence of the characters, a collection of element arrangements are concatenated together to form the complete bar code symbol, with each character of the message being represented by its own corresponding group of elements. In some symbologies, a unique xe2x80x9cstartxe2x80x9d and xe2x80x9cstopxe2x80x9d character is used to indicate when the bar code begins and ends. A number of different bar code symbologies is in widespread use including UPC/EAN, Code 39, Code 128, Codabar, and Interleaved 2 of 5.
In order to increase the amount of data that can be represented or stored on a given amount of surface area, several more compact bar code symbologies have been developed. One of these code standards, Code 49, exemplifies a xe2x80x9ctwo-dimensionalxe2x80x9d symbol by reducing the vertical height of a one-dimensional symbol, and then stacking distinct rows of such one-dimensional symbols, so that information is encoded both vertically as well as horizontally. That is, in Code 49, there are several rows of bar and space patterns, instead of only one row as in a xe2x80x9cone-dimensionalxe2x80x9d symbol. The structure of Code 49 is described in U.S. Pat. No. 4,794,239. Another two-dimensional symbology, known as xe2x80x9cPDF417xe2x80x9d, is described in U.S. Pat. No. 5,304,786.
Still other symbologies have been developed in which the symbol is comprised not of stacked rows, but of a matrix array made up of hexagonal, square, polygonal and/or other geometric shapes, lines, or dots. Such symbols are described in, for example, U.S. Pat. Nos. 5,2276,315 and 4,794,239. Such matrix code symbologies may include Vericode, Datacode, and MAXICODE.
Various optical scanning systems and readers have been developed heretofore for reading indicia such as bar code symbols appearing on a label or on the surface of an article. The readers function by electro-optically transforming the spatial pattern represented by the graphic indicia into a time-varying electrical signal, which is in turn decoded into data which represent the information or characters encoded in the indicia that are intended to be descriptive of the article or some characteristic thereof. Such data is typically represented in digital form and utilized as an input to a data processing system for applications in point-of-sale processing, inventory control distribution, transportation and logistics, and the like.
One particularly advantageous type of reader is an optical scanner which scans a beam of light, such as a laser beam, across the symbols. Laser scanner systems and components have generally been designed to read indicia having parts of different light reflectivity, i.e., bar code symbols, particularly of the Universal Product Code (UPC) type, at a certain working range or reading distance from a hand-held or stationary scanner to the symbol or target.
In the laser beam scanning systems known in the art, a single laser light beam from a light source is directed by a lens or other optical components along a light path toward a target that includes a bar code symbol on a target surface. The moving-beam scanner operates by repetitively scanning the light beam in a line or a series of lines across the symbol by means of motion of a scanning component, such as the light source itself or a mirror disposed in the path of the light beam. The scanning component may either sweep a beam spot across the symbol and trace a scan line across the symbol, or scan the field of view of a sensor of the scanner, or do both. The laser beam may be moved by optical or opto-mechanical means to produce a scanning light beam. Such action may be performed by either deflecting the beam (such as by a moving optical element, such as a mirror) or moving the light source itself. U.S. Pat. No. 5,486,944 describes a scanning module in which a mirror is mounted on a flex element for reciprocal oscillation by electromagnetic actuation. U.S. Pat. No. 5,144,120 to Krichever et al. describes laser, optical and sensor components mounted on a drive for repetitive reciprocating motion either about an axis or in a plane to effect scanning of the laser beam.
Another type of bar code scanner employs electronic means for causing the light beam to be deflected and thereby scan a bar code symbol, rather than using a mechanical motion to move or deflect the beam. For example, a linear array of closely spaced light sources activated one at a time in a regular sequence may be transmitted to the bar code symbol to simulate a scanned beam from a single source. Instead of a single linear array of light sources, a multiple-line array of individual lasers may also be employed, thereby producing multiple scan lines. Such type of bar code reader is disclosed in U.S. Pat. No. 5,258,605 to Metlitsky et al. The use of multiple discrete lasers is also described in U.S. Pat. No. 5,717,221.
Bar code reading systems also include a sensor or photodetector which detects light reflected or scattered from the symbol. The photodetector or sensor is positioned in the scanner in an optical path so that it has a field of view which ensures the capture of a portion of the light which is reflected or scattered off the symbol, detected, and converted into an electrical signal.
In retroreflective light collection, a single optical component, e.g., a reciprocally oscillatory mirror, such as described by Krichever et al. in U.S. Pat. No. 4,816,661 or by Shepard et al. in U.S. Pat. No. 4,409,470, both herein incorporated by reference, and U.S. Pat. No. 6,114,712, scans the beam across a target surface and directs the collected light to a detector. The mirror surface usually is relatively large to receive as much incoming light as is possible. Only a small detector is required since the mirror can focus the light onto a small detector surface, which increases signal-to-noise ratio.
A variety of mirror and motor configurations can be used to move the beam in a desired scanning pattern. For example, U.S. Pat. No. 4,251,798 discloses a rotating polygon having a planar mirror at each side, each mirror tracing a scan line across the symbol. U.S. Pat. Nos. 4,387,297 and 4,409,470 both employ a planar mirror which is repetitively and reciprocally driven in alternate circumferential directions about a drive shaft on which the mirror is mounted. U.S. Pat. No. 4,816,660 discloses a multi-mirror construction composed of a generally concave mirror portion and a generally planar mirror portion. The multi-mirror construction is repetitively reciprocally driven in alternate circumferential directions about a drive shaft on which the multi-mirror construction is mounted. U.S. Pat. No. 6,247,647 describes an arrangement for providing either a multiple line, or a single line, scan pattern by means of a controller. All of the above-mentioned U.S. patents are incorporated herein by reference.
In electro-optical scanners of the type discussed above, the implementation of the laser source, the optics, the mirror structure, the drive to oscillate the mirror structure, the photodetector, and the associated signal processing and decoding circuitry as individual components all add size and weight to the scanner. In applications involving protracted use, a large, heavy scanner can produce user fatigue. When use of the scanner produces fatigue or is in some other way inconvenient, the user is reluctant to operate the scanner. Any reluctance to consistently use the scanner defeats the data gathering purposes for which such bar code systems are intended. Thus, a need exists for a compact module to fit into small compact devices, such as electronic notebooks, portable digital assistants, pagers, cell phones, and other pocket appliances, which can serve multiple scanning applications.
Thus, an ongoing objective of bar code reader development is to miniaturize the reader as much as possible, and a need still exists to further reduce the size and weight of the scan engine and to provide a particularly convenient to use scanner. The mass of the moving components should be as low as possible to minimize the power required to produce the scanning movement, thereby saving battery power.
It is further desirable to modularize the scan engine so that a single module can be used in a variety of different scanning applications, such as a single scan line and a raster scan line pattern. A need exists to develop a particularly compact, lightweight module which contains all the necessary light source, scanner and photosensor components for both applications. A further need exists to permanently visually indicate when a bar code reader has been exposed to mechanical shock.
Objects of the Invention
It is an object of the present invention to provide a single module capable of selectable single line or rastering scanning motion of the light beam for use in a bar code reader.
A related object is to develop an electro-optical scanning module which is both smaller and lighter in weight than using discrete components, while providing a collector area of at least 20 mm2.
It is yet a further object to produce a module which may be manufactured conveniently, and at low cost.
Another object is to permanently visually indicate when a reader has been exposed to mechanical shock.
Features of the Invention
Briefly, and in general terms, the present invention provides an optical scan module including a base; a light source supported by the base, for generating and directing a light beam along a first segment of a first optical path; a first scan assembly in the first optical path including a reciprocally oscillatable, first scan mirror mounted for receiving the light beam and sweeping the beam in a first direction at a first frequency; an optical assembly including a light collector for collecting and re-directing light reflected from a symbol along a second optical path, the second path having an optical axis that is displaced from said first segment of the first optical path; a second scan assembly in the second optical path including a reciprocally oscillatable, second scan mirror mounted for oscillating movement, and operative for receiving the light beam along the second optical path, and for sweeping the beam in a second direction at a second frequency along a third optical path exteriorly of the module; and a sensor supported by the base for detecting the collected reflected light that has been re-directed by the light collector, and for generating an electrical signal corresponding to the detected light intensity.
The present invention further provides an optical scanner for reading an optical code symbol having either a one-dimensional or a two-dimensional pattern of different light reflectivity, including a first and a second light source for producing first and second laser light beams; and a scanning assembly for receiving one of the light beams and producing a respective outgoing light beam having either a one-dimensional or a two-dimensional scanning pattern.
According to the invention, there is further provided a retroreflective optical scan module, including first and second selectable light sources having different beam characteristics for directing a selected light beam to a symbol to be read, an optical assembly including a light collector which collects and redirects the light reflected from the symbol along an optical path to a sensor, and means for selecting which light source to use depending on whether a one-dimensional or a two-dimensional symbol is being scanned.
According to the invention, there is further provided a small-size optical scan module in the form factor of a substantially rectangular parallelepiped module having dimensions approximately 30 mmxc3x9715 mmxc3x977.5 mm. In the first embodiment, on one of the larger sides (i.e., preferably a peripheral side measuring 30 mmxc3x9715 mm, there is mounted thereon a light source for emitting a light beam, first and second scanning assemblies for receiving said light beam and for generating therefrom a scanning beam directed to an indicia to be read, a detector, and a collector mirror arranged to receive reflected light and to direct it to the detector.
The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. Further features of the invention are set out in the appended independent claims, and further preferred features are set out in the dependent claims.